FIELD OF THE INVENTION
A first aspect of the present invention relates to a method of sintering cement clinker of a type using a spouted-type fluidized bed granulating furnace and a fluidized bed sintering furnace and a sintering apparatus for use to embody the sintering method.
A second aspect of the present invention related to an apparatus for discharging granules from a fluidized bed for cement clinker, such as a spouted-type fluidized bed granulating furnace or a fluidized bed sintering furnace.
A third aspect of the present invention relates to a cement clinker sintering apparatus having an improved discharge chute for injecting, into a sintering furnace, substances granulated in a granulating furnace of a spouted bed type or a spouted-type fluidized bed type or a fluidized bed type.
A fourth aspect of the present invention relates to an apparatus for sintering cement clinker comprising an improved discharge chute of a granulating furnace of a spouted bed type or a spouted-type fluidized bed type or a fluidized bed type.
Cement clinker is manufactured in such a manner that raw material powder obtained by blending and grinding limestone or quartz sand is first granulated and then it is sintered and cooled. In recent years, the cement clinker has been usually manufactured by using a sintering apparatus comprising a spouted-type fluidized bed granulating furnace and a fluidized bed sintering furnace. The reason for this is that the cement sintering apparatus using the fluidized bed furnace exhibits excellent heat efficiency and advantages in terms of reducing required installation space, realizing a satisfactory fuel consumption and preventing harmful gases (NOX and CO2 and so forth) as compared with a conventional rotary kiln type sintering apparatus. Moreover, the foregoing furnace is considered suitable to manufacture many types of products in a small quantity. In addition, an apparatus of the foregoing type comprising the two furnaces as the essential portion thereof enables the granulating process and the sintering process to be individually controlled, causing an advantage to be obtained in that cement clinker exhibiting excellent quality can be manufactured.
In the spouted-type fluidized bed granulating furnace, raw material powder, which has been previously heated and injected to the same, is fluidized by hot gas so that a portion of the fluidized raw material powder present adjacent to the surface is, with heat, melted and allowed to adhere mutually as to be allowed to grow to granules (granulated substances) having a diameter of several millimeters. However, the size of each granule (that is, the granule size) must adequately be arranged to be adaptable to the specifications of the facility and the type of desired cement. If the granule size is too large, the granulated substances cannot easily be fluidized in the granulating furnace and the ensuing sintering furnace, causing a problem to arise in that burning and sintering and the like cannot properly be performed. If the granule size is too small, the adhesion of the granules proceeds excessively in the sintering furnace, and therefore an undesirable phenomenon that is so called agglomeration takes place. As a result the quality of the cement clinker deteriorates and, what is worse, the operation of the sintering apparatus (for example, control of the temperature) cannot easily be performed and the heat efficiency deteriorates.
Under these circumstances, it is necessary that a portion of the substances granulated in the granulating furnace that has been enlarged to have granule sizes larger than a predetermined size must be classified and injected into the sintering furnace. A classifying means of the foregoing type has been disclosed in Japanese Patent Unexamined Publication No. 62-228875. According to this disclosure, a granulating furnace formed into a spouted bed type (a type of fluidized bed) and a fluidized bed sintering furnace are directly connected to each other while interposing a throat portion (a passage through which spouted gas flows) to adequately control the velocity of the spouted gas flow from the sintering furnace to the granulating furnace. As a result, only granules that have a granule size larger than a predetermined size are dropped from the granulating furnace to the sintering furnace by way of the throat portion to improve the classifying efficiency.
A sintering apparatus of a type that has not two furnaces for granulating and sintering has been disclosed in Japanese Patent Publication No. 44-32193, the apparatus being arranged in such a manner that an extracting chute having a function capable of classifying granules (sintered granules) is disposed on a center line passing in the lower portion of the furnace body (a sintering furnace also serving as a granulating furnace).
The foregoing two disclosed structures cannot enable satisfactory results to be obtained in terms of the controllability of the granule size and quality of the granules. Experiments and studies recently performed by the inventors of the present invention resulted in the knowledge that the means according to the former disclosure (Japanese Patent Unexamined Publication No. 62-228875) is insufficient to accurately classify granules to satisfy the quality level desired recently because an excessively large quantity of granules drops (so called "direct drop") from the throat portion to the sintering furnace even if granules smaller than a predetermined granule size are present. The reason for this can be considered as follows: since the throat portion serving as a passage through which gas for forming the spouted bed flows has a large diameter (hundreds of millimeters), the velocities of gas flowing in the cross section of the throat portion are distributed (deviated) considerably. Further, commencement of the drop causes the gas velocity in the throat to be changed. Therefore, it is difficult to uniformly classify the granulated substances with respect to a predetermined granule size. Since the latter technology (Japanese Patent Publication No. 44-32193) is arranged in such a manner that granulating and sintering are performed in one furnace, the quality of the products is inferior to that obtainable from a typical sintering apparatus (having no classifying function) comprising the two furnaces regardless of the classifying precision. Further, the granule extracting chute, which can be disposed in a relatively low temperature portion in the one-furnace-type apparatus, must be disposed in a hot portion of about 1300.degree. C. in the two-furnace-type apparatus. Therefore, the technology of the foregoing disclosure cannot easily be adapted to the two-furnace-type sintering apparatus (a first problem).
As an apparatus for discharging granules from a spouted bed furnace, such as a spouted-type fluidized bed granulating furnace or a fluidized bed sintering furnace, the following apparatus is exemplified:
For example, a structure (of a so-called "bottom flow type") has been suggested which is, as shown in FIG. 15, constituted in such a manner that the granules are injected from a discharge chute 104 disposed in the side wall adjacent to the bottom of a granulating furnace 103 into a fluidized bed sintering furnace 107 disposed below the granulating furnace 103 by way of a discharge chute 105 and a so-called L-valve 106 (hermetic discharge apparatus).
However, the foregoing structure causes the granules in the discharge chute to not move actively in a manner similar those in the granulating furnace bed but form a moving bed, resulting in that the granules which are partially melted with heat are allowed to adhere together in the discharge chute adjacent to a discharge port. Moreover, adhesion of the granules to the wall surface of the discharge chute causes the discharge chute to be blocked, resulting in that the discharge of the granules cannot be stably maintained. As a result, there arises a problem in that the operation cannot be stably performed.
As a structure for injecting granules graded in the granulating furnace 103 into the fluidized bed sintering furnace 107, structures respectively disclosed in Japanese Patent Publication No. 44-32193 and Japanese Patent Unexamined Publication No. 62-228875 have been suggested. Each of the foregoing structures is arranged in such a manner that the throat portion between the granulating furnace 103 and the fluidized bed sintering furnace 107 is used as a discharge port or a discharge port is formed to adjust the flow velocity so as to selectively drop large granules into the sintering furnace 107.
However, the foregoing structures encounter reduction in the flow rate of air in the discharge port with the commencement of dropping of large granules, causing all granules in the granulating furnace 103 to be undesirably dropped into the sintering furnace 107. Further, the control becomes too complicated.
In order to overcome the foregoing problems, a group including the applicant of the present invention has applied an apparatus for sintering cement clinker arranged in such a manner that one of nozzle hole of a perforated distributor disposed in the throat portion is used as a passage through which the granules drop and a means for controlling the quantity of spouted gas passing through the nozzle hole is provided as exemplified by a gate which can be opened/closed and which is disposed in the opening portion at the lower end of the nozzle hole (Japanese Patent Application No. 4-360488).
However, the foregoing apparatus is arranged in such a manner that the gate is opened/closed to control the flow velocity to enable the granules to be discharged intermittently sometimes encounters a problem in that the granules are allowed to adhere to the nozzle hole at the time of closing the gate, resulting in a problem to arise in that the function as the discharge apparatus cannot be exhibited sometimes (a second problem).
Hitherto, an apparatus for sintering cement clinker has employed a structure as shown in FIG. 17. That is, raw material powder for cement injected through a raw material injection chute 201 is previously heated by a suspension pre-heater 202 composed of cyclones 200C.sub.1, 200C.sub.2 and 200C.sub.3 when the raw material powder for cement sequentially passes through the cyclones 200C.sub.1, 200C.sub.2 and 200C.sub.3. The pre-heated raw material for cement is injected into a granulating furnace 203 of a fluidized bed type or a spouted bed type, and granules granulated in a fluidized manner or a spouted manner in the granulating furnace 203 are injected into a fluidized bed sintering furnace 207 disposed below the granulating furnace 203. The granules sintered in the fluidized bed sintering furnace 207 as described above are allowed to pass through a fluidized bed cooler 208 and a moving bed cooler 209 as to be recovered finally as cement clinker. It should be noted that reference numeral 200A.sub.1 represents a heavy oil supply line.
In order to inject the granules granulated in the granulating furnace 203 into the fluidized bed sintering furnace 207, structures respectively disclosed in Japanese Patent Publication No. 44-32193 and Japanese Patent Unexamined Publication No. 62-228875 have been suggested. The foregoing structures are arranged such that the throat portion between the granulating furnace 203 and the fluidized bed sintering furnace 207 is used as a discharge port or a discharge port is formed to adjust the flow velocity so as to selectively drop large granules into the sintering furnace 207.
However, the foregoing structures encounter reduction in the flow rate of air in the discharge port with the commencement of dropping of large granules, causing all granules in the granulating furnace 203 to be undesirably dropped into the sintering furnace 207. Further, the control becomes too complicated.
In order to overcome the foregoing problems, a structure (of a so-called "bottom flow type") has been suggested which is, as shown in FIG. 18, constituted in such a manner that granules are injected from a discharge hole 204 formed in the side wall adjacent to the bottom portion of the granulating furnace 203 into the fluidized bed sintering furnace 207 disposed below the granulating furnace 203 by way of the discharge chute 205 and a so-called L-valve (a hermetic discharge apparatus). The foregoing structure employs a structure for preventing blockage of the discharge chute, the structure being constituted in such a manner that the discharge chute 205 and the portion adjacent to the discharge port of the furnace are indirectly cooled by a cooling jacket 204a into which a cooling medium, such as air or water, is introduced by blowing or the same is directly cooled (refer to Japanese Patent Unexamined Publication No. 62-233677 and so forth).
However, the foregoing structure causes the granules in the discharge chute to not move actively in a manner similar to those in the granulating furnace bed but form a moving bed, resulting in that the granules partially melted with heat are allowed to adhere mutually in the discharge chute adjacent to the discharge port. Moreover, adhesion of the granules to the wall surface of the discharge chute causes the discharge chute to be blocked, resulting in that the discharge of the granules cannot be stably maintained. As a result, there arises a problem in that the operation cannot be stably performed. That is, direct or indirect cooling of the wall surface of the discharge chute cannot cool all granules. What is worse, mixture with granules in the granulating furnace bed inhibits satisfactory cooling of the granules in the discharge chute, causing a problem to arise in that the blockage cannot completely be prevented (a third problem).
As another conventional technology, an apparatus for sintering cement clinker has been disclosed in, for example Japanese Patent Unexamined Publication No. 62-233677. According to the foregoing disclosure, there has been suggested an apparatus arranged in such a manner that raw material powder for cement previously heated by a pre-heating means composed of a suspension pre-heater is injected into spouted bed type or a spouted-type fluidized bed or a fluidized bed type granulating furnace as shown in FIG. 19 as to be granulated, and the granules are, by way of a discharge chute connected to the granulating furnace bed, injected into a fluidized bed sintering furnace as to be sintered, wherein a chute for discharging hot granules graded in the granulating furnace or the chute and the portion adjacent to the discharge port formed in the granulating furnace are directly or indirectly cooled by a cooling medium so as to prevent blockage of the discharge chute by the granules (see, for example, Japanese Patent Unexamined Publication No. 62-233677).
The foregoing conventional disclosure about a discharge apparatus arranged in such a manner that the discharge port is formed in the bed of the granulating furnace as shown in FIG. 19, and the granules are charged into the discharge chute and the granules are injected into the sintering furnace by way of the L-valve (the hermetic discharge apparatus) while maintaining a material seal results in the granules in the discharge chute not actively moving similar to those in the bed in the granulating furnace. The granules partially melted with heat for the purpose of forming a moving bed are allowed to mutually adhere in the discharge chute adjacent to the discharge port, and granules allowed to adhere to the wall surface of the discharge chute block the discharge chute. As a result, there arises a problem in that a stable discharge flow of granules cannot be maintained, and therefore the operation cannot be stably performed. As described above, the structure comprising discharge port formed in the bed of the granulating furnace encounters the unsatisfactory limitation of the granules that can be cooled even if the granules present adjacent to the discharge port are cooled directly with cooling air or the same is indirectly cooled while interposing the wall surface of the discharge chute. What is worse, mixture with the granules in the bed of the granulating furnace inhibits satisfactory cooling of the granules in the discharge chute, and accordingly a problem arises in that the prevention of the blockage cannot completely be performed (a fourth problem).